master cylinder help

[reborn55]

Master cylinder on wife's coupe needs to be replaced--small leak. Thought it was from 76 Nova---car has later model Nova clip--calipers, rotors etc. So I ordered brand new one for a 76 Nova---looked identical, painted it all up, bench bled it, installed it and no fluid tot he rear brakes. Tried to re bleed it at master cylinder, very little to no fluid came out of the rear port. Bad master cylinder or wrong valving inside of the unit. The one I ordered fits from 71-77 Nova, Chevelle etc. Casting number-6470409 come back as 70 Chevelle but none of the ones I have found look the same. I thought most setups would work--old cylinder works great--just a little weepage at the rear of it and around the gasket. Any help would be appreciated..Thanks a lot.  appreciate it

[Harry]

I could be wrong...but isn't the rear port on the M/C for the front brakes?

[reborn55]

Mine has large reservoir(disc) and small in teh back for drums(rear)

[kb426]

Is the proportioning valve stuck to one side? How about the line from the frame to the rear axle being collapsed ? I'm not familiar with 76 Nova's, is there something different from the earlier versions on the length of the master cylinder so the pushrod isn't retracting enough to allow the rear port to be open?

[enjenjo]

Did you bench bleed it?

[reborn55]

The master cylinder pictured works properly--just leaks a little at rear piston and gasket.  the one I replaced it with looks exactly like the pictured one but I cannot enough fluid out the rear port to the rear brakes.  that is what I am trying to figure out.

[reborn55]

yep--bench bled it---thinking it might be a bad cylinder--hate to get another one and find it the same.

[kb426]

Someone on here has bought one that wasn't done properly and blocked a port. I don't remember any details.

[wayne petty]

let try something..


do you have any wheel alignment shims...

1/16" thick or 1/8" thick...

for a test ONLY.. do not drive it this way...

loosen the 2 master cylinder mounting nuts...  slide it away from the brake booster.... slip in the 1/16" wheel alignment shims between the booster face and the master.. so the master sits a tiny amount farther forward...

lightly snug the mounting nuts back down..

there are various depths of the push rod hole..  sometimes the push rod is sticking up too far...

i have also found the brake pedal pivot bushing was worn and not allowing the brake pedal to return..

i have found the threaded plunger type brake light switch that was misadjusted and was holding the pedal slightly down...

when the master cylinder piston is in the fully seated position against the snap ring.. both ports in the reservoir should be uncovered...


hint... and its a PAIN...

i start with the lines into the master disconnected..

my fingers or thumbs over both openings as i have somebody pump the pedal lightly...  once i get fluid flowing during the pump. but stopping the air from sucking back in with my fingers.. i am now ready to hook up the brake lines to the master again...

there is a chance that that overseas as they all are.. masters were assembled wrong..   when you only make 25 cents an hour and the boss screams at you constantly... you put things together wrong when you can..

[BFS57]

Hello;
Breaks on a tri five!? a subject I know all too well!!!!
First off, the combination you have is correct. Second, There are lots of "adjustments" on these combinations! Be aware, a little bit goes a long way!
Had a recent problem after installing a power steering box on my 57. the shop had to take the brake lines off to do the deed. then, no brakes at all they bled and bled but still no brakes, then they broke out a power suction device and hooked it to the bleeder (front, but would work on the rear as well. After several attempts, something finally happened and brake fluid came out like gang busters! So in effect you may have crud in the line going to the rear brakes (drum?).
There is many adjustments including the booster pin to the MC. This must be adjusted right or problems can happen! Unfortunately, brake parts from off shore are totally junk. I hope you are starting off with a NEW MC not a rebuilt one! Be aware that if the new MC is not adjusted right to the booster it can lead to "dragging" brakes that overheat, the fluid expands, and you are going nowhere!!  
It's important to have the same size bore as the MC you removed, if the old unit had a 1" bore the new should have the same. Don't trust the parts store to give you the correct part, you have to know what you want any more because our cars aren't made by honda
I know how you feel! I've had new MC that didn't work and had to replace it with another that did work! This was from a pretty reputable on line supplier (Pirate Jack) They sent me a replacement and up graded it to aluminum with a Stainless insert!
I'm sorry if I may have gone over some subjects you may be fully aware of and hope that some of my experiences can help you get your problems straightened out!
I can't begin to tell you how many hours I have spent "learning" about this subject!

Bruce

[wayne petty]

11 pages of brake master cylinder training manual

http://www.autoshop101.com/forms/brake02.pdf

17 pages on brake booster

http://www.autoshop101.com/forms/brake05.pdf


5 or 6 on brake diagnosis..

http://www.autoshop101.com/forms/brake07.pdf

this section covers the brake safety valve, proportioning valves and other ways to control brake bias...

http://www.autoshop101.com/forms/brake08.pdf


should take less than 30 minutes for the first 2 sections..

[reborn55]

well got another new master cylinder today and the same problem--upon a little close inspection I found that there is a stop screw in the front reservoir that is on the coupe and the new one doesn't have it.  Push rod stroke is also different.  So tomorrow I am going to try a master cylinder that has the Delco casting number(which I have evidently) and see what happens.  Kind of hit or miss when you don't buld it yourself--thanks for help

[reborn55]

All fixed--Bought a Delco master cylinder--bench bled--installed screw stop and installed---brakes great no leaks and happy wife--she is driving 150 miles to a show this weekend.--thanks

[papastoyss]

All fixed--Bought a Delco master cylinder--bench bled--installed screw stop and installed---brakes great no leaks and happy wife--she is driving 150 miles to a show this weekend.--thanks

"Happy wife, happy life", got 44 yrs in & counting.